Non raster image scanning

ABSTRACT

A method is described for scanning image pixels in a sequence which, in contrast to the traditional and ubiquitous raster scan, better groups effectively adjacent and neighbouring image pixels together in the scanned sequence, resulting in a much lower bandwidth signal and leading directly to bandwidth and storage gains from compression and exploitation of image redundancy. M-Scan, for meandering scan, is synthesised by iterative application of a simple primitive pattern or patterns, and analysed by iterative partitioning. M-Scans can achieve unbroken continuity between pixels in the image, and in routine application never need to step between non image adjacent pixels. Whereas a conventional raster has a low vertical and a high horizontal scan rate, M-Scan has intermediate and approximately equal vertical and horizontal rates. An M-Scan signal power spectrum lacks the comb at the line rate of the conventional raster scan signal. An M-Scan approaches image details from diverse directions and does not exhibit spectacular ghosting failure under spurious reflections like raster scans. M-Scans can be used for 3 dimensional images, or time series 2D images, whilst still preserving adjacent pixel connectivity. The M-Scan deflection signals place greatly reduced and near minimised demands on the deflection means, in contrast to conventional raster signals whose upper speed and required slew rates virtually rule out mechanical deflection means for large displays.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] Foreign Priority is claimed through this Information: Country Application Number Filing Date Priority Claimed Australia 13554/02 Jan. 25, 2002 Yes

[0002] Australian Complete Specification (i.e. non provisional) Standard Patent Non Raster Image Scanning application number 13554/02, was filed in Sydney on Jan. 25 2002.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0003] Not applicable.

REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISK APPENDIX

[0004] Not applicable.

BACKGROUND OF THE INVENTION

[0005] 1. Images in the context of contemporary communications, storage and analysis technologies are inevitably, at some or at many stages along their path from source to observer, considered as being composed of a vast number of pixels, or very tiny points, each having a single color and brightness. These points are usually placed on a microscopically square grid, with a large rectangular extent encompassing the whole image.

[0006] 2. Alternative representations not doing this could be of vector or polygon type, and the term “non raster”, outside this specification, could commonly or usually be used to refer to non scanned image representations possibly of those or related types. Herein, the term “non raster” refers to a different scanning method, and not to non scanned graphic representations.

[0007] 3. Under the prior art, the large rectangle of pixels has been scanned, or placed in sequence, by simply following the grid of straight horizontal lines from left to right across the image, then flying back or retracing to the left again, to the start of the next line just underneath the previous, and so on to the bottom of the image, then retracing to the top. Double spacing or interlacing has commonly been used to reduce flicker. On display, the flyback or retrace portions are normally blanked and not visible. The associated deflection signals, which comprise sequences of the deflection coordinates, or the coordinates of the current pixel, have discontinuities or sharp spikes in their first and second derivatives, and need high bandwidth because of these retraces. The associated video signal, which is the sequence of scanned pixel values, generally contains discontinuities at the retrace boundaries, independent of the deflection signals.

BRIEF SUMMARY OF THE INVENTION

[0008] 4. In this invention, a method of scanning is disclosed which eliminates the large, disruptive and spectrally demanding discontinuities from the image signal, and also from the deflection signals.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0009] 5. FIG. 1 shows a scan primitive related to a conventional raster scan, a scan using this primitive synthesised in the manner of M-Scan, and a conventional built up raster scan, not synthesised in that way but rather by distorting the primitive.

[0010] 6. FIG. 2 shows the M-Scan 2-primitive, which is the principal foundation of M-Scan, and one step in building up a larger image scan using it.

[0011] 7. FIG. 3 shows how the popular aspect ratios of 4:3 and 16:9 can be treated at the top level allowing M-Scans to be used at the lower levels.

[0012] 8. FIG. 4 shows how a 4:3 image can be scanned using only the 2-primitive and its scans, which isn't true of the method indicated for this in FIG. 3.

[0013] 9. FIG. 5 shows the M-Scan 3-primitives, the need for which was implied in the first method of FIG. 2, and one step in building up a larger image scan using them.

DETAILED DESCRIPTION OF THE INVENTION

[0014] 10. This invention defines an improved method of scanning images, without the use of a conventional raster. This scanning method is called M-Scan, after meandering, which describes the behaviour of the scan in contrast to the traditional raster.

[0015] 11. The points or pixels that make up an image are conventionally scanned in a raster pattern, which has a series of horizontal lines connected by flyback lines. In raster scanning adjacent image pixels are scanned together (i.e. consecutively) only if they are horizontally adjacent (or possibly terminating a flyback line). Vertically adjacent pixels are separated by at least a whole line in a conventional raster scan.

[0016] 12. In oversampled images with high pixel redundancy, a minimum bandwidth scanned image signal can only be produced if adjacent pixels are scanned together as much as possible. A conventional raster scan fails to achieve this well.

[0017] 13. This invention describes a method of scanning which does not use a conventional raster, which more effectively groups adjacent pixels in scanning, and which yields a signal of much reduced bandwidth than the conventional raster, especially for highly redundant or oversampled images. This M-Scan signal is much better suited to subsequent transmission through a limited bandwidth channel, to economical storage, and to other processing such as compression using for example run length encoding, than a raster scan signal.

[0018] 14. Recursive partitioning is a principal feature of M-Scan analysis.

[0019] 15. The M-Scan for a large square image can be analysed through recursive partitioning. A large square image is first partitioned into four equally sized smaller square images. These four are taken in an order given by a primitive pattern or sequence, and are, in a further iteration, themselves partitioned in the same way. By repeatedly subjecting the outputs of partitioning to further division, the analysis is extended from the full image down to the level of pixels, whose sequence is the full image scan.

[0020] 16. A synthetic approach leading from the pixel level primitive up to the full image M-Scan complements the above analysis. In synthesis, the M-Scan primitive is replicated, rotated and connected and re-applied, but its shape is unaltered.

[0021] 17. To first take the conventional raster, the primitive sequence which is a 4 pixel raster scan is shown at the left of FIG. 1.

[0022] 18. FIG. 1: Primitive raster sequence or pattern, its synthesised scan, and 16 pixel conventional raster scan

[0023] 19. To analyse, the 16 pixel image (synthesised scan, centre of FIG. 1) is partitioned into four images of 4 pixels, each of which is scanned according to the primitive sequence on the left. The four are processed in sequence, shown by interconnection, as per the primitive. [A conventional raster scan, shown on the right, does not conform to and is not a solution of this analysis.] To synthesise, four of the primitives are taken, arranged in the same pattern, and interconnected, forming the synthesised 16 pixel scan. A 64 pixel scan could be similarly synthesised by taking 4 of the 16 pixel scans, and so on, leading to a scan of 2** (2n) pixels for any desired positive integer n.

[0024] 20. The conventional raster is not built up by iterated synthesis on a constant primitive, but by altering or deforming the raster primitive, as FIG. 1 illustrates.

[0025] 21. The principal primitive sequence on which M-Scan is based is a non raster sequence, can be used under recursive partitioning/synthesis to generate a full M-Scan, and is illustrated in FIG. 2.

[0026] 22. FIG. 2: M-Scan primitive sequence (the 2-primitive), and one synthesis thereon

[0027] 23. To analyse, the image of 16 pixels is partitioned into four images of 4 pixels, each of the four is scanned according to the primitive sequence on the left, but with an internal orientation chosen to achieve connectivity with both the preceding and succeeding partitions. Together with the constraint that scan start and finish remain at opposite ends of the same side, a unique synthesised scan results. By iteration of the synthesis implied in the above analysis, the M-Scans for any square image with 2** (2n) pixels can be generated, for any positive integer n.

[0028] 24. The M-Scans achieve a connectivity between partitions which could not be achieved with the raster scan of FIG. 1. This connectivity eliminates from the M-Scans the jumps between non adjacent image pixels and their associated steps or discontinuities in the scan signal, and means that M-Scan signals have a much lower bandwidth than raster scan signals. Ten times narrower bandwidth at the −60 dB points of power spectral density could be achieved, before the additional use of any other compression or bandwidth conservation means. The comb-like line structure dominant in the raster scan signal spectrum is absent from the M-Scan signal spectrum. Because of this characteristic, analogue signals carrying M-Scanned images of similar quality could be reasonably packed about 8 times closer together in frequency than their raster scan equivalents.

[0029] 25. Under M-Scan, features in the image are approached and scanned in different directions, and so images are not degraded with predominantly horizontal blurring under bandwidth limitations or low pass filtering of the scan signal, as occurs with conventional raster scan. Similarly a spurious echo in transmission does not cause a single coherent and obvious image ghost as in raster scan.

[0030] 26. FIG. 3 shows how images of aspect ratios 4:3 and 16:9 can be readily analysed at the top level into square partitions which can then be further subject to direct M-Scan analysis as described above, whilst enabling continuity between partitions to be retained as before, avoiding scan jumps between nonadjacent image pixels, even at frame endpoints, and minimising scan signal bandwidth. The curves are a shorthand indication, locating the start and end points of scan for that square. The M-scan for a square is uniquely determined by the location of the end points, and the resolution, if only the 2-primitive is used.

[0031] 27. FIG. 3: 4:3 and 16:9 aspect ratio images partitioned with connectivity preserved

[0032] 28. However the top level scan of the 4:3 aspect ratio image of FIG. 3 cannot be performed with subscans based exclusively on the 2-primitive, because one of the squares shown has a side three times longer than another—for the method of FIG. 3 the 3-primitive is needed.

[0033] 29. A method of scanning a 4:3 aspect ratio image using only the 2-primitive is shown in FIG. 4. The 4 by 3 image is scanned as two 2 by 2 squares and four 1 by 1 squares, each of which can be further subdivided with successive 2 by 2 analysis, obviating the need for the factor 3.

[0034] 30. FIG. 4: Analysis of an image with 4:3 aspect ratio to use only 2-primitive M-scans

[0035] 31. At the right of FIG. 5 the M-scan 3-primitives are shown. These are not unique given the endpoints; there is a choice of 2, and hence during scan synthesis, many implementations are possible due to these choices. One way of choosing the “best” option is to maximise the number of corners.

[0036] 32. FIG. 5: 3-primitive M-scan analysis and synthesis; left relates to upper right

[0037] 33. A scan built on the 3-primitive has fewer corners, is less tight, and does not meander as effectively as a scan using the 2-primitive. The average number of comers per scanned pixel is lower.

[0038] 34. Nevertheless, the judicious use of the 3-primitive pattern, probably at one of the upper level (i.e. closer to the whole image) scan or analysis layers, can ease the restriction on available image pixel dimensions, otherwise experienced through exclusive use of the 2-primitive pattern.

[0039] 35. Higher level primitives can be defined, but the utility and effectiveness is already taken by the 2-primitive possibly augmented with the 3-primitive, and the higher order primitives are hence not expected to be advantageous in most applications.

[0040] 36. Three dimensional images can be scanned in one form of this invention through a sequence of 2 dimensional M-Scans, with endpoints joined (i.e. corresponding to adjacent pixels in the 3D image) thus preserving connectivity and minimising signal bandwidth. In another form of this invention a 3 dimensional M-Scan can be built up in a cube of eight sub cubes, retaining connectivity, with each sub cube containing either a primitive or a sub-scan, in synthesis analogous to the 2D M-Scan synthesis described above. In another form of this invention a time series of 2D images is scanned with a 3D M-Scan as though the series formed a 3D image, thus exploiting the redundancy associated with oversampling in time.

[0041] 37. Digital encoding of image information allows adaptive change of parameters such as sampling pitch in all dimensions including time, quantisation resolution, centre value, range from maximum to minimum, and linearity/nonlinearity of quantisation method.

[0042] 38. Traditional raster scanning and M-Scanning can be used in a static, data independent mode in which scanning proceeds at a constant rate, but in another form of this invention M-Scans are used in adaptive or dynamic methods of scanning, where different parameter sets may be used in image partitions, or in partial image processing, to enable image approximations of varying levels of detail, accuracy and bandwidth requirements to be transmitted or processed. In one particular form of this invention, 1 and a half or 2 bit quantisation is performed on an image, which is then M-Scanned, processed, stored in a compact data set and transmitted, and the image is subsequently further processed and improved in selected or priority areas with higher resolution in any or all spatial/time sampling and signal quantisation, again using M-Scanned image data over the target regions desired for further improvement within the image. The crude, coarse, low information density image could for example represent many frames of a uniformly coloured tennis court, with the target areas including projectiles and relevant court lines. The rationale behind this approach is to create the best perception of detail and image quality, whilst making more economical use of bandwidth or data transmission capacity or other scarce and limiting resources. 

The claims defining this invention are as follows:
 1. A method of image scanning, or of placing all the image pixels of a regularly sampled rectangular two or higher dimensional image into an ordered sequence or into a time based signal, which uses, instead of a conventional raster, a scanning sequence built up by recursive applications of a simple primitive sequence, which primitive and all its built up sequences have the property that any 2 consecutive pixels or partitions in the scanned sequence are adjacent pixels or partitions in the image.
 2. A method of generating a bandwidth compressed scan signal of an image for transmission or for subsequent processing and transmission in a limited bandwidth channel using a scanning method of claim
 1. 3. A method of transforming the data comprising the pixels of an image into a more compact set of data, possibly with further data compression, using a scanning method of claim
 1. 4. A method of rendering an image transmission less susceptible to ghosting from transmission echoes by using a scanning method of claim
 1. 5. A method of selective rather than homogeneous image scanning, with a scanning method of claim 1 applied to various chosen parts or manipulated versions of an image or images, with possibly differing scanning parameters, to more quickly or economically process coarse, low resolution information or unprioritised versions of an image or images, thereby allowing more scarce resources to be devoted to higher importance parts of the image, leading to increased perceived quality with the limited resources available.
 6. A method of claim 5 used for minimising signal bandwidth as in claim
 2. 7. A method of claim 5 used for minimising storage requirements as in claim
 3. 8. A large screen display and its method of implementation employing the deflection methods and signals described herein reducing and minimising the speed and jerkiness of movement and associated demands placed on the deflection means or mechanism, creating a scanning display system achieving relatively high resolution, high contrast and intensity, whilst exploiting and taking full advantage of the smoother and slower deflection signals described herein. 